This invention relates to an apparatus for controlling magnetic field intensity of electromagnetic lenses or charged particle beam deflection means used in a charged particle beam apparatus such as an electron microscope, an X-ray microanalyzer, a device for electron beam exposure, or other similar charged particle beam devices.
Electromagnetic lenses and deflecting means in an X-ray microanalyzer and the like incorporate ferromagnetic yokes disposed adjacent to the excitation coils through which coils the excitation current flows. Different lens powers (focal lengths) or deflection powers may be obtained with the very same excitation current supplied to the same lens coils or deflection coils, because of the hystersis of the ferromagnetic yokes. Therefore, it is necessary to deal with the effect due to the hysteresis of the lens or deflection means when the apparatus is to be controlled by a computer.